1. ¹ML Research, Keele University Science Park, Keele, Staffordshire ST5 5SP, UK
2. ²YCR Cancer Research Unit, Department of Biology University of York, York Y010 5YW, UK
3. ³CR UK Institute for Cancer Studies, Clinical Research Block, University of Birmingham, Birmingham B15 2TT, UK

Correspondence: Kai S. Lipinski, Fax: +44 (0)1782 714 167. E-mail: kai.lipinski@mlresearch.co.uk

^†Present address: Institute for Pathology, Karl-Franzens-University, Auenbruggerplatz 25, A-8036 Graz, Austria.

Received 27 March 2004; Accepted 27 March 2004.

Abstract

We recently published the construction and evaluation of a -catenin-dependent, highly active promoter, CTP1, and its possible application for the treatment of colorectal cancer using gene-directed enzyme prodrug therapy with adenoviral (Ad) vectors. Alternative Ad-based approaches such as tumor-specific, replication-competent vectors and/or exploiting therapeutic gene products with intrinsic toxic activity, such as gibbon ape leukemia virus fusogenic membrane glycoprotein, diphtheria toxin A (DTA), and ricin, would demand a very tightly regulated promoter to avoid breakthrough replication and toxicity in nontumor tissue and Ad producer cell lines. In this study we optimized the activity/specificity profile of the synthetic -catenin-dependent promoter by varying its basal promoter, the number of Tcf binding sites, and the distance between these and the basal promoter. The optimal promoter, CTP4, showed virtually undetectable expression in cells with normal -catenin regulation but high level expression in cells deregulated for -catenin. Using CTP4 we were able to generate, for the first time to our knowledge, an Ad vector expressing fully active wild-type DTA without the need for time-consuming and cumbersome production systems. CTP4 should be the promoter of choice for Ad-based gene therapies of tumors deregulated for -catenin. We provide preliminary evidence that these may include prostate and ovarian as well as colorectal cancer.